O'Reilly— Notes on some Assays for Gold, etc. 455 



debris carried down by the streams in consequence of their decom- 

 position, must have carried in its bed golden sands, and may 

 retain in the lowest stratum of the gravels and sands in contact 

 with the mother rock quantities of gold worthy of serious explora- 

 tory works. Some further assays of rock samples from this 

 neighbourhood would seem to support this view. 



Thus, the steam tram line to Blessington, which runs along 

 the foot of the Saggart Hills, passes into the Brittas valley across 

 a bridge which I believe is known in the country as the Crookling 

 or Crooked Bridge, and the hill to the east of it is known locally 

 as Crookling Hill. The formation is clay slate of the lower 

 Silurian, containing here and there ribs of quartz, and traversed 

 in several places by lenticular masses of diorite of the same 

 nature as the stone of Bohernabreena, which circumstance led 

 to their being worked for road metal. In one of the old quarries 

 where one of these diorite masses occurs there are parts showing 

 large detached crystals of iron pyrites. A certain quantity of 

 these were separated from the containing rock and a sample sub- 

 mitted for assay, the return being 6 grains to the ton of 20 cwt. 

 At the same time, samples of the rock as it came from the quarry 

 were ground and submitted for assay in three different states of 

 fineness of division. In each of these traces of gold were found, 

 the amount in one of them being 2 grains per ton of 20 cwt. 



In respect to these pyrites it may be of interest to cite the 

 observation of the celebrated chemist J. B. Boussingault, which 

 appears in a Memoir by him on " A New Method of Assaying and 

 Treating Auriferous Pyrites," An. d. Mines, 1827, p. 319. At p. 

 330 he says : " As regards auriferous pyrites it is less important to 

 know exactly the richness of the ore than to determine the presence 

 of gold in it, since once demonstrated that it is auriferous it is 

 quite certain that it is well worth while being worked." 



It is of interest to note that this diorite mass is traversed by a 

 vertical vein of quartz, about 12 to 14 inches wide, and having a 

 direction of N. 9° 53 E., a not unfrequent direction of joining in 

 the environs of Dublin. Lastly, on the course of the Kiver Liffey, at 

 a point about one mile to the south of Blessington, there is a bridge 

 in the close vicinity of a ruin known as " Bogey's Castle." The 

 river here bends and gives rise to a small strand, where are thrown 

 up during floods pebbles of different sizes, many of them being 



SCIEN. FROC. R.D.S. VOL. VI., PART VIII. 2 M 



